In recent years, wireless communication has been increasingly required to have higher capacity and higher speed, so that it has been actively studied to further improve utilization efficiency of finite frequency resources. Of the various methods developed so far, the use of the spatial domain is drawing attention.
One of the spatial domain techniques is to use adaptive array antennas (adaptive antennas). In this technique, a received signal is multiplied by a weighting coefficient to adjust its amplitude and phase. This allows to strongly receive a signal that is intended to be received (hereinafter, a “desired signal”) and to suppress the interference signal, thereby reducing co-channel interference and increasing system capacity.
Another of the spatial domain techniques is to use spatial orthogonality in a propagation path. In the technique, different data sequences are transmitted to different terminals using physical channels having the same time, the same frequency, and the same sign.
Spatial division multiplexing transmission technology is described, for example, in non-patent document 1 (T. Ohgane et al, “A study on a channel allocation scheme with an adaptive array in SDMA”, IEEE 47th VTC, pages 725-729, vol. 2, 1997). A wireless base station device and terminals for spatial division multiplexing transmission based on this technology can perform spatial division multiplexing transmission if the spatial correlation coefficient between the terminals is lower than a predetermined value. This improves the throughput of the radio communication system and the concurrent user capacity.
However, in such a conventional structure, the wireless base station device is required to detect a spatial correlation coefficient between the terminals and to select the terminals having a spatial correlation coefficient smaller than the predetermined value as the terminals to be connected by spatial division multiplexing (hereinafter, this selecting operation is referred to as “allocation”).
Furthermore, the spatial correlation coefficient is required to be detected and updated frequently or periodically because it has the nature of varying with time due to changes in the propagation environment associated with the movement of the terminals or surrounding objects. This complicates both the detection of a spatial correlation coefficient and the allocation of the terminals to be connected by spatial division multiplexing, thereby increasing the processing delay associated therewith.